34 replies to this topic

[briandmiller]

I just realized that the fan does turn off during the initial period when the thermostat calls for heat while the burner is turning on and getting warmed up and then the fan comes back on and stays on. Does this indicate something else to look at as the source of the fan staying on or is that happening somewhere else in the schematic?

[jb8103]

A component should be isolated from the circuit for a reliable resistance check.

I don't have the literature for this Rheem model. The Owner's Manual and/or Installation Manual should have a section on sequence of operation. The IFC (circuit board) has timing circuits. The sequence should go something like this: on a call for heat, the IFC confirms all limit switches are closed. It signals the IDR. The Induced Draft Motor starts. The pressure switches make. The IFC confirms the pressure switches then signals the Ignition Relay. The Ignition Element heats up. After, say, 30 seconds, the IFC signals the Gas Valve Relay. The gas valve opens and the burners ignite. The IFC confirms at least 5 microamps DC from the Flame Sensor. The IFC starts another timer, say 60 seconds to allow the heat exchanger to heat up to about 140F or so, then signals the Blower Relay, which starts the Indoor Blower Motor (the fan). When the thermostat is satisfied, the Gas Valve is closed, the Induced Draft Motor is shut off and the pressure switches open. But the Indoor Blower Motor stays on according to the timer controlled by the DIP switches on the IFC. That's the little red switch block with white switches at the upper center of the IFC, they can be manually set. It will stay on for 60 or 120 or 180 seconds or something similar, to extract the residual heat from the heat exchanger, then the IFC opens the Blower Relay and the blower stops. In your case it's not stopping.

But let's back up a bit.

I just realized that the fan does turn off during the initial period when the thermostat calls for heat...

Have you turned off the service disconnect, then turned it back on? Or has the fan been running in between calls for heat and only shuts off for a while when the thermostat makes?

Edited by jb8103, 02 October 2011 - 10:53 PM.

[briandmiller]

Have you turned off the service disconnect, then turned it back on? Or has the fan been running in between calls for heat and only shuts off for a while when the thermostat makes?

The latter. The fan runs in between calls for heat and only shuts off for a while when the thermostat makes?

The furnace had sat idle all summer in auto mode but the fan started running constantly one day last week without the thermostat ever calling for heat. after that I had the service disconnect turned off in between testing but hadn't witnessed the fan stopping during the initial call for heat as I now have.

[jb8103]

In that case I believe the Blower Relay is functional, and that there is something else goofy in the IFC.

There is also the remote possibility that your thermostat wires have shorted somewhere along its unseen length. I would disconnect them from the terminal strip at the furnace also, at least the green wire.

[briandmiller]

I disconnected all of the wires from the terminal strip at the furnace end before opening this thread so that's not it. If there isn't anything other than the board that could be causing this then I can go ahead and replace the board. Just would like to know that would do it.

[jb8103]

If I'm 100% confident about anything, it's death and taxes.

Let me put it this way, we've seen no evidence of anything faulty outside the Black Box. My next move would be to replace it, but I could be wrong.

[jb8103]

with the 24v 2A Fuse near the Controller removed,
OR with either of the 24v power wires to the Controller removed,
Turn power ON...
Does the Fan still run ? (shorted Relay Contacts)

Also did you run this test? It will help prove the Black Box is bad, before you spend hundreds on a new one.

[RegUS_PatOff]

I just realized that the fan does turn off during the initial period when the thermostat calls for heat while the burner is turning on and getting warmed up and then the fan comes back on and stays on. Does this indicate something else to look at as the source of the fan staying on or is that happening somewhere else in the schematic?

looks like a bad Controller

[briandmiller]

Also did you run this test? It will help prove the Black Box is bad, before you spend hundreds on a new one.

In reviewing this post I realized that I had not done this correctly. I had only removed the wires from the thermostat, not the power wires. I just went back and pulled the fuse off the board and the fan does not come on in this state. Any clues on what that tells us?

[RegUS_PatOff]

looks like a bad Controller

[briandmiller]

I'l know soon. ordered one from Amazon. Should be here today.

[jb8103]

In reviewing this post I realized that I had not done this correctly. I had only removed the wires from the thermostat, not the power wires. I just went back and pulled the fuse off the board and the fan does not come on in this state. Any clues on what that tells us?

Actually I quoted the wrong post from Reg. I wanted the one asking for voltage across the relay. But anyway, if the limit switches proved to be closed, and with the blower turning off at start of sequence proving the relay is functional, with the thermostat wires out of the circuit, with the IFM, valve and burners working as advertised, there's nothing else left that I can think of.

[briandmiller]

New board got the furnace running fine. Thank you all for your help.

Now I just need to figure out what's going on with my Honeywell TrueSTEAM humidifier.

[Dan Webster]

Glad you could git her done

[jb8103]

New board got the furnace running fine. Thank you all for your help.

Now I just need to figure out what's going on with my Honeywell TrueSTEAM humidifier.

But...there can't possibly be anything wrong with a Honeywell TrueSTEAM humidifier!